1. Technical Field of the Invention
The present invention relates to cellular communications systems and, in particular, to such systems implementing multiple hyperband communications capabilities.
2. Description of Related Art
North American cellular communications have historically been implemented solely in the 800 MHZ Cellular hyperband. This Cellular hyperband is assigned two telephone frequency bands (commonly referred to as the A frequency band and the B frequency band) for carrying communications. The A and B frequency bands include the paging, control and other associated signaling channels necessary for setting up and maintaining cellular telephone calls, as well as the voice channels that are provided for carrying subscriber telephone communications.
Each frequency band within the Cellular hyperband is typically assigned to only one service company and is provided in the service area by that service company. For example, the A frequency band is usually reserved for use by non-wire line communications service companies, and the B frequency band is usually reserved for use by wire line communications service companies. In some instances, the particular communications frequency band (A or B) within the Cellular hyperband assigned to one service company for a given cell or service area may be assigned to a different service company in another cell or service area. Furthermore, in some cases the same service company will provide cellular communications service across both frequency bands. Alternatively, the individual channels within one frequency band may be assigned to different companies. The assignment of channels, frequency bands and hyperbands to service providers is dependent upon many factors including, for example, the size of the service area, the number of potential subscribers and the number of contracting providers.
The most recent evolution in cellular communications services involves the adoption of hyperbands other than the Cellular hyperband for handling mobile station communications. In accordance with the EIA/TIA Interim Standard IS-136 described in TIA project number PN3011 (the "IS-136 specification"), and specification PN3388-1 version Sep. 9, 1994, four different hyperbands have now been specified for use in handling mobile communications. These hyperbands comprise the Cellular hyperband previously in use and described briefly above, the Personal Communication Services (PCS) hyperband which has been established in the 1900 MHZ frequency range, and two other hyperbands that are currently reserved for future use but are not yet fully specified in terms of their operating characteristics.
Whereas the Cellular hyperband includes two frequency bands (A and B), the PCS hyperband in the United States of America is specified to include six different frequency bands (A, B, C, D, E and F). Thus, in accordance with the current IS-136 and PN3388 specifications, eight frequency bands (including multiple channels therein) are now available in any given service area to facilitate cellular communications services. With the existence of the new PCS hyperband, different types of subscriptions and/or services like speech quality, voice privacy, and encryption may exist from one hyperband to another, or from one frequency band in the Cellular hyperband to another frequency band in the PCS hyperband.
Reference is now made to FIG. 1 wherein there is shown a cell diagram illustrating an exemplary cell configuration for implementing multiple hyperband cellular communications services over an arbitrary geographic area (hereinafter "the service area") in accordance with the current IS-136 and PN3388 specifications utilizing both the Cellular and PCS hyperbands. The service area is divided into a plurality of cells 10 and 20. The cells 10 are represented by hexagrams and comprise communications cells wherein as many as two separate frequency bands (A and B) of radio frequency cellular communications are provided via multiple channels in the Cellular hyperband. The cells 20, are represented by circles and comprise communications cells wherein as many as six separate frequency bands (A through F) of radio frequency cellular communications are provided to mobile stations via multiple channels in the PCS hyperband.
In some instances, the Cellular hyperband cells 10 and the PCS hyperband cells 20 will be co-located, as generally shown at 12, and further may have comparable communications coverage areas, as generally shown at 14. Such cell characteristics, however, are not requirements for operation of a multiple hyperband communications system in accordance with the IS-136 and PN3388 specifications. Thus, different cell center locations and instances of overlapping cell coverage areas between the hyperbands will be a common occurrence, as generally shown at 16 and 18, respectively. Furthermore, it will often be the case that the combined communications coverage areas provided by all or part of two or more Cellular hyperband cells 10 will be contained within the coverage area of a single PCS hyperband cell 20, as generally shown at 22. Similarly, it is possible that the combined communications coverage areas provided by all or part of a PCS hyperband cell 20 will be contained within the coverage area of a single Cellular hyperband cell 10, as generally shown at 24.
Each of the Cellular hyperband cells 10 includes at least one base station 26 configured to facilitate communications over certain channels in at least one of the two available Cellular hyperband frequency bands. It is possible, and in fact may be preferred, for each of the cellular base stations 26 to possess the capability of communicating over both the A and B frequency bands of the Cellular hyperband. Similarly, each of the PCS hyperband cells 20 includes at least one PCS base station 28 configured to facilitate communications over certain channels in at least one of the six available PCS hyperband frequency bands. As with the cellular base stations 26, it is possible, and in fact may be preferred, for each of the PCS base stations 28 to possess the capability of communicating over more than one, and perhaps all six, of the frequency bands of the PCS hyperband. Although not shown in the figure for reasons of simplifying the illustration, in instances where a base station 26 or 28 does not provide coverage for all of the available hyperbands and/or the frequency bands therein, more than one base station will be needed in each cell. Furthermore, more than one base station may be needed per cell if there is a division of communications responsibility between service providers on a per channel basis.
The base stations 26 and 28 are illustrated as being positionally located at or near the center of each of the cells 10 and 20, respectively. However, depending on geography and other known factors, the base stations 26 and 28 may instead be located at or near the periphery of, or otherwise away from the centers of, each of the cells 10 and 20. In such instances, the base stations 26 and 28 may broadcast and communicate with mobile stations located within the cells 10 and 20 using directional rather than omni-directional antennas. Each one of the base stations 26 and 28 includes a transmitter, a receiver, and a base station controller connected to the antenna in a manner and with a configuration well known in the art.
Each one of frequency bands specified for the Cellular and PCS hyperbands is allocated a plurality of voice or speech channels and at least one access or control channel. The voice or speech channels carry subscriber telephonic communications. The control channel is used to control or supervise the operation of mobile stations by means of information transmitted to and received from the mobile stations. Such information may include incoming call signals, outgoing call signals, page signals, page response signals, location registration signals, voice channel assignments, maintenance instructions, and cell selection or reselection instructions as a mobile station travels out of the radio coverage of one cell and into the radio coverage of another cell. The control or voice channels may operate either in an analog or digital mode or a combination thereof.
Many mobile stations having Cellular hyperband only communications capabilities were purchased prior to the adoption of the new multiple hyperband IS-136 and PN3388 specifications and are currently in use. These Cellular hyperband only capable mobile stations do not possess the functionality to access and communicate over, and thus fully take advantage of, the PCS hyperband. Accordingly, multiple hyperband capable mobile stations possessing communications capabilities in both the Cellular and PCS hyperbands have been developed and are now being placed into service in order for subscribers and providers to take full advantage of the hyperbands (and frequency bands therein) made available by the new IS-136 and PN3388 specifications.
Reference is now made to FIG. 2. In accordance with the new IS-136 specification, each mobile station functioning in idle operating mode receives from the cellular communications system a neighbor list 30 identifying the channels available to the mobile station for server selection. This neighbor list is transmitted to each mobile station over the control channel. In order to account for the availability in the service area of the PCS hyperband and the frequency bands therein, the server selection neighbor list 30 transmitted to each mobile station must include an identification of the channels available to the mobile station in both the Cellular (n1) and PCS (n2) hyperbands.
Unfortunately, the IS-136 specification allows for a maximum of twenty-four channels across both available hyperbands (n1+n2&lt;=24) to be included in the server selection neighbor list 30 processed by each mobile station. The n2 portion of the server selection neighbor list 30 identifying available PCS hyperband channels is, however, of no use to Cellular hyperband only capable mobile stations which cannot communicate over the PCS hyperband channels. The inclusion of PCS hyperband channels in the server selection neighbor list 30 further serves to displace from the list certain (n2 in number) available Cellular hyperband channels that otherwise would have been provided for selection to the Cellular hyperband only mobile stations.
A similar problem under the IS-136 specification is presented when the mobile stations are functioning in an on call operating mode. In this case, the mobile station receives from the cellular communications system a MAHO neighbor list 32 identifying the channels the system wants the mobile station to scan for, measure on and report on periodically for purposes of making hand-off determinations. This MAHO neighbor list 32 is transmitted to each mobile station over the voice channel, and is determined from the hyperband capabilities of the mobile station and the channels identified in the neighbor list 30. A Cellular hyperband only capable mobile station will receive a MAHO neighbor list 32 which includes an identification of channels from the neighbor list 30 only in the Cellular hyperband. A multiple hyperband capable mobile station, on the other hand, will receive a MAHO neighbor list 32 identifying channels from the neighbor list 30 in both the Cellular and PCS hyperbands. It should be understood that the previous description specific to IS-136 is also applicable to its counterpart PN3388 specification.
Accordingly, there is a need for a cellular communications system having multiple hyperband communications capabilities that will make more efficient use of the limited number of entries allowed by the IS-136 and PN3388 specifications in both the server selection and MAHO neighbor lists. Such a system will provide relevant, useful and sufficient information not only to those mobile stations that are capable of operating across multiple hyperbands, but also to the large number of Cellular hyperband only capable mobile stations that are currently in use by cellular subscribers.